The art is repleat with staplers that close a generally U-shaped staple by bending spaced parts of a central portion of the staple around the surfaces of an anvil so that projecting legs of the staple will engage and join adjacent materials (such as portions of disunited skin) adjacent the anvil, whereupon the anvil can be withdrawn from within the closed, generally rectangular, staple which will then hold the materials together.
Typically, the anvil in such a stapler projects from a planar guide surface for the staple, and has surfaces around which a staple is to be bent disposed generally at right angles to the guide surfaces. These anvil surfaces include opposite edge surfaces spaced at a distance corresponding to the distance between the spaced parts of the staple to be bent, and a contact surface extendng transverse of the passageway between the edge surfaces adopted to engage the central portion of the staple between the spaced parts to be bent. Means are provided for positioning a staple at the anvil with the central portion of the staple extending across the contact surface, the parts of the staple to be bent during closing at the edges where the contact surface and edge surfaces meet, and the legs of the staple projecting along the edge surfaces and the guide surface. A rim having a side surface positioned along the guide surface has an end portion adjacent the anvil, which end portion has spaced tip portions with a generally U-shaped opening therebetween defined by end surfaces on the ram disposed generally at right angles to the guide surface. The end surfaces on the ram include an innermost surface generally parallel and opposed to the contact surface on the anvil, and opposed side surfaces generally parallel to the edge surfaces on the anvil and spaced apart a distance exceeding the distance between the edge surfaces by about twice the thickness of the central portion of a staple. The ram is mounted on the housing for movement from a first position affording positioning a staple along the guide surface adjacent the anvil, to a formed position with the side surfaces of the ram opposite the edge surfaces of the anvil and the innermost surface of the ram adjacent the contact surface of the anvil to close the staple by bending its central portion around the anvil.
Such a stapler adapted for use in the medical field is described in U.S. patent application Ser. No. 14,911 filed Feb. 26, 1979 now U.S. Pat. No. 4,202,480. The stapler described in that application is activated by manually squeezing together toggle linkages on opposite sides of the path for the ram to move the ram to its formed position so that it will close the staple around the anvil.
While the staples described in that application normally work with good reliability, the possibility has existed that a staple could become displaced along the anvil away from the guide surface as the staple was clossed due, perhaps, to the staple being closed into a material it could not penetrate (such as metal) or other external forces. In extreme cases, such displacement could even cause the end surfaces of the plunger to become scored so that the scoring in the plunger would cause subsequent staples closed by the stapler to move away from the guide surface along the anvil, and thus not to be properly closed. While various approaches have been used to correct this problem such as hardening the end portion of the ram and/or longitudinally grooving the ram along its side surfaces to guide the portions of the staples bent around the anvil and prevent such scoring, or disposing the contact surface of the anvil at a slight acute angle with the guide surface to bias the central part of the staple to the intersection between the guide surface and the contact surface of the anvil, these approaches have either been expensive, have not been entirely successful in solving the problem, or have presented additional problems.